1. Field of the Invention
The present invention relates to a non linear circuit for open load control in Low-Side Driver type circuits.
2. Discussion of the Related Art
Modem integrated circuits, having switches placed on the ground side, called Low-Side Drivers, usually contain some checking circuits adapted for signaling malfunctions caused by load separation, a situation known as open load in the technical literature.
These checking circuits point out not only the load existence, and therefore also the absence, when the power transistor placed at the output is turned off but also when the transistor is turned on.
In the case that the power transistor is turned off, the load absence condition, that is the open load condition, is verified by the output voltage measurement, while in the case that the power transistor is turned on the current flowing in the power transistor must be measured and checked to see if this current is less than a predetermined value of the threshold current, a value describing the open load.
The problem consists, therefore, in the measurement of this threshold current, that flows in the power transistor, and also in the correct signaling of the open load.
In view of the state of the art described, it is an object of the present invention to measure the threshold current with precision so as to avoid uncertainty situations about the load condition, this resulting from measuring the threshold current with circuit elements not depending on the power transistor.
According to the present invention, this and other objects are achieved by a non linear circuit for open load control in Low-Side Driver type circuits, comprising at least two power transistors, scaled according to an area ratio 1 to M, with M greater than 1, wherein the power transistor having the smaller area is controlled by a circuit input signal while the transistor having the larger area is controlled by the output value of an AND type logic gate managed by a control circuit, that is regulated by the output value of a voltage sensor placed in parallel with the power transistor having the larger area, and by the output value of a current sensor placed in series with the power transistor having the smaller area, so that, when a current flowing in the power transistor having the smaller area is less than a predetermined value of the threshold current, the control circuit signals the open load on an output pin.
As a result of the present invention it is possible to make a circuit for open load checking in a Low-Side Driver type circuit when this circuit is turned on, having the maximum precision in evaluating the load leakage limit current and eliminating circuit instability drawbacks because there are no reaction loops including linear circuits to be compensated.